1. Field of the Invention
The present invention relates to a gas compressor, and specifically to an improvement of an oil separator which centrifuges oil from a compressed gas discharged from a compressor.
2. Description of the Related Art
An air conditioning system has used a gas compressor for compressing a gas such as a coolant gas and thus circulating the compressed gas in the air conditioning system.
A compressor generally includes a compressor unit compressing and discharging a gas; and an oil separator separating oil such as refrigeration oil from the compressed coolant gas discharged from this compressor unit.
A known oil separator includes an outer cylindrical unit including a substantially columnar space with a closed bottom end surface by an end wall having an oil discharging passage; and an inner cylinder portion in a substantially cylindrical form provided inside the outer cylindrical unit and being almost coaxial with the substantially columnar space of the outer cylindrical unit. This type of oil separator centrifuges refrigeration oil from the compressed coolant gas by allowing rotating compressed coolant gas to flow through a substantially cylindrical space (an oil separating space) defined by the inner surface of the outer cylindrical unit and the outer surface of the inner cylinder portion (See Japanese Unexamined Patent Application Publication No. 2007-327340).
The inner cylinder portion and the outer cylindrical unit are separate parts. The inner cylinder portion is fixed to the outer cylindrical unit by press-fitting or caulking. Thereby, the inner cylinder portion and the outer cylindrical unit are integrated to be the oil separator.
The compressor changes the rotation speed in accordance with a desired output from the air conditioning system. During a high speed rotation, the coolant gas flows at a very high speed through the oil separating space of the oil separator, so that the compressor unit exhibits a better oil separation performance that in the normal operation.
With the improvement in oil separation performance, an amount of the refrigeration oil (or oil content rate (OCR)) to be discharged together with the coolant gas from the gas compressor to the air conditioning system is decreased. The less the amount of refrigeration oil discharged to the air conditioning system (condenser), the less the amount of refrigeration oil returned together with the coolant gas to the gas compressor from the air conditioning system (evaporator). This decreases the amount of refrigeration oil mixed in the coolant gas to be suctioned into compression chambers, which accordingly reduces the amount of refrigeration oil to be introduced into the compression chambers together with the coolant gas. Accordingly, with a reduction in the amount of refrigeration oil as the coolant, the temperature of the coolant gas discharged from the compression chambers is increased, resulting in decreasing the volumetric efficiency.
In order to prevent this problem, during high speed rotation of the compressor, prevention of excessive decrease in the OCR is required.